The present invention is directed to a computer readable storage medium for controlling engine torque using feedback and feed forward control.
Electronic airflow control systems, such as variable cam timing systems and electronic throttle control systems, replace traditional mechanical throttle cable systems with an xe2x80x9celectronic linkagexe2x80x9d provided by sensors and actuators in communication with an electronic controller. This increases the control authority of the electronic controller and allows the airflow and/or fuel flow to be controlled independently of the accelerator pedal position.
To control the actual output engine brake torque to achieve the driver demanded engine brake torque, it is desirable to calculate a corresponding desired airflow and fuel flow. Preferably, this computation accounts for variations in engine operating parameters, such as engine operating temperature and accessory losses.
Prior art approaches convert the desired engine torque to a desired airflow using a two-dimensional lookup table with inputs for desired torque and engine speed. However, such lookup tables are typically calibrated for stoichiometric operation and for maximum brake torque (MBT). The resulting desired airflow is then modified by a function which relates engine operating temperature and air/fuel ratio to engine torque to generate a modified or corrected airflow. The corrected desired airflow is then achieved via an appropriate airflow rate controller. This approach may be seen by reference to U.S. Pat. Nos. 5,351,776 and 5,383,432, for example.
While the prior art approaches may be acceptable for many applications and operating conditions, it is desirable to provide a more robust engine torque controller which improves powertrain performance for current applications and is more amenable to new engine technologies and control strategies such as direct injection, lean burn, variable cam timing, and variable displacement applications.
It is an object of the present invention to provide a computer readable storage medium having stored data representing instructions for controlling engine torque in an engine having electronically controlled airflow and/or fuel flow.
Another object of the present invention is to provide engine torque control which more accurately compensates for current operating conditions such as additional frictional losses when the engine is cold and for variable accessory losses which correct for variations between desired and actual torque using a torque feedback signal.
In carrying out the above object and other objects, advantages, and features of the present invention, a computer readable system and method for controlling engine torque includes instructions for determining a desired engine brake torque based on accelerator pedal position, barometric pressure, and speed; instructions for adjusting the desired engine brake torque to generate a requested engine brake torque based on current operating conditions; and instructions for controlling at least one operating parameter of the engine based on the requested engine brake torque to deliver the desired engine brake torque. Preferably, the desired engine brake torque is modified by combining the desired engine brake torque with an idle speed torque to generate a first intermediate torque, comparing the first intermediate torque to an actual engine brake torque to generate a second intermediate torque, generating a feedback correction torque based on the second intermediate torque, and combining the first intermediate torque, the feedback correction torque, and a third intermediate torque to determine the requested engine brake torque, where the third intermediate torque represents accessory load or a frictional torque loss which varies with temperature.
The present invention provides a number of advantages over prior art control strategies. The present invention compensates the input to the engine torque controller prior to determination of the control parameters, such as airflow and fuel flow, rather than modifying the output of the engine torque controller as described in the prior art. This provides a more robust torque controller which is more easily applied to various engine technologies.
The above advantages and other advantages, objects, and features of the present invention, will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.